Biaxial loading of pre-cracked cruciform testpieces has been preformed in a novel rig attached to a uniaxial testing machine. Fracture toughness R or delta(c) of the ductile acrylonitride butadiene styrene (ABS) and polyvinyl chloride (PVC) determined by the Cotterell-Mai method is dependent on remote biaxiality. Least toughness is shown for equibiaxial tension; greatest for uniaxial tension. These monotonic fracture results may be modelled using void growth mechanics. Fatigue crack growth rates also depend on remote biaxiality. Paris/Walker representation of the data shows that the slopes n of log (d aid N) versus log Delta K do not change much, but the constant of proportionality C decreases as the tensile mean stress increases. There may be a connection between the biaxial-dependent C and R or delta(c).